The present invention relates to a safety closing system for a shaft door panel of an elevator installation.
Elevator installations generally have different kinds of doors, namely on the one hand a car door by which the car is closable and on the other hand shaft doors, wherein a shaft door is present for any and every accessible interruption of the elevator shaft. These doors consist of one or more door panels.
The door panels, especially the shaft door panels, are usually so constructed that they are suspended at corresponding elements of the elevator shaft in the region of the panel upper edge and are guided in the region of the panel lower edge. The panel upper edge is usually constructed so that the movement of the shaft door is a rolling movement, whilst the panel lower edge executes a guided sliding movement or, in a given case, a contactless movement.
In normal operation a shaft door is opened and closed in each instance synchronously with the car door, wherein the shaft door and the car door during the opening and closing process are mechanically connected together by an entrainer coupling. The doors of the elevator installations and, in particular, the shaft doors are for reasons of safety constructed to be self-closing. By that there is to be understood that the shaft doors are equipped with a safety closing system which always brings the door panel into a closed setting when no forces act to bring the door panel into an open setting against the force exerted by the safety closing system or to keep it in a wholly or partly opened open setting. The safety closing system has to be effective not only when the elevator car is disposed outside a floor to which the car is traveling, but also in certain special situations, particularly in the case of failure of the power supply. The safety closing system thus must be actuable by forces that are effective even in the case of power failure and in other emergency situations, for example in the event of a fire.
Conventional elevator installations therefore have shaft doors or shaft door panels with safety closing systems that are mechanically actuated.
A safety closing system, which was frequently used in the past, for a shaft door panel employs, as a drive, a weight or the force which acts, as a consequence of gravity, on a drive mass. The line of action of this force is vertical, whereas the shaft door panel usually has to be moved in a horizontal direction. A deflection is therefore carried out with the help of a roller mechanism and a flexible traction element.
The substantial advantage of such a safety closing system with a vertically arranged drive mass resides in the fact that gravity virtually cannot be reduced or excluded in any case, so that the safety closing system or at least its drive remains effective in every instance.
However, this safety closing system has certain disadvantages intrinsic to the system. Fundamentally, the drive mass, so that it can be effective at all, is a comparatively high mass which firstly has to be accelerated so that the closing process at the start takes place sluggishly. Whereas the force acting on the shaft door panel is—at least without taking account of the friction—constant, the speed at which the shaft door panel is brought into the closed setting increases during the closing process. This has the consequence that the shaft door panel firstly moves only slowly, but at the end of its movement path drops at high speed into the closed setting and is abruptly stopped there. If the undoubtedly present friction is initially taken into consideration, it has to be established that this is greatest at the beginning of the action of the door closing system. Then, in fact, it is necessary to overcome the stiction that is present, for example, between the moved shaft door panel and the non-moved frame parts. If the shaft door panel is in motion, then only a motional friction still has to be overcome, namely a sliding friction or a rolling friction depending on the respective construction of the shaft door panel. So that the shaft door panel can even be brought into movement, the drive mass must thus be of such a size that the stiction can be overcome, because at the moment at which the shaft door panel has to be set in motion there are still no dynamic forces acting thereon, but only the weight of the drive mass. Moreover, the risk exists that the shaft door panel does not move as intended, but jams in whatever manner so that an appropriately higher force has to be employed for movement thereof. A specific disadvantage of a safety closing system with a drive mass can thus be seen in that a deflecting device is required, because the weight always has a vertical effect, whereas the movement of the shaft door panel generally takes place in horizontal direction.
Another frequently used safety closing system employs, as drive for the safety closing system of a shaft door panel, one or optionally several mechanical tension springs. The tension springs in that case are installed in such a manner that they are relieved or adopt their rest position in the closed setting of the shaft door panel. The opening of the shaft door panel takes place against the action of the spring. On opening of the shaft door panel, the tension spring is stretched and thus tensioned. If a force which seeks to bring the shaft door panel into its open setting no longer acts, then the spring relaxes and thereby brings the shaft door panel into its closed setting. Springs can, in fact, have different characteristics, but without special measures the spring force increases with increasing deflection or change in length and reduces with decreasing deflection or change in length. The greatest force thus acts on the shaft door panel when it adopts its open setting, because at this instant the spring is deflected to the greatest extent from its rest position or tensioned. While the shaft door panel moves under the action of the spring to its closed setting, the spring force reduces.
The springs can be so arranged that the line of action of the force exerted by them is horizontal, whereby a deflection by a roller mechanism and a flexible traction element is redundant. Frequently, however, the springs are so installed that the line of action of the force exerted by them is vertical, so that a deflection has to be provided as in the case of safety closing systems with drive masses.
A safety closing system with a spring as drive means has, by comparison with an arrangement which uses a drive mass or a weight as drive, advantages and disadvantages.
One advantage resides in the fact that a spring has a relatively low mass so that it does not have a high level of inertia. It is particularly advantageous that the force exerted by a spring on the shaft door panel is at its greatest when the shaft door panel adopts its open setting and has to be set into motion. During the closing process the spring relaxes and the force exerted on the shaft door panel diminishes. It is thereby achieved that with suitable selection of the spring the stiction acting on the open shaft door panel is overcome in relatively problem-free manner and that the speed of the shaft door panel constantly diminishes the closer it comes to its closed setting. If in the selection of the spring characteristic the motional friction is additionally taken into consideration, then it can be achieved that the speed of the shaft door panel towards the end of its closing movement is almost constant. In this manner it is possible to avoid, without additional braking or damping equipment, the shaft door panel dropping into its closed setting at high speed and having to be abruptly stopped there. A further advantage of a safety closing system with a spring can be seen in that the spring can be installed in such a manner that the line of action of the force exerted by it is horizontal and thereby coincides with the direction of movement of the shaft door panel, so that a corresponding deflecting mechanism is redundant. However, a horizontally installed tension spring which is not too stiff has to be efficiently guided.
The disadvantages of a spring as drive for a safety closing system of a shaft door panel reside in the fact that springs are more susceptible to failure in different ways than drive masses. Due to material deficiencies springs can have characteristics different from those assumed, they can fatigue particularly after over-stretching and they can break after, for example, a defined number of load changes. It is also disadvantageous for their function within a safety closing system that the spring characteristics change in certain circumstances, for example, in dependence on temperature. If no special measures are undertaken, the risk also exists that the shaft door panel does not fully reach its closed setting when these springs are relaxed. However, it can be attempted to avoid this by biasing the springs to a certain extent in the closed setting of the shaft door panel.
In summary, it has to be established that satisfactory safety closing systems for shaft door panels can be produced neither with drive masses nor with springs.